It is known to stabilize polycarbonates with boric acid esters as per U.S. Pat. Nos. 3,321,435 and 3,404,122.
It is also known to stabilize polycarbonates with oxetane compounds as per U.S. Pat. Nos. 3,794,629 and 4,073,769 and German Published Patent Specification No. 2,658,849 which corresponds to U.S. patent application Ser. No. 644,934 filed Dec. 24, 1975, to Axelrod.
It is also known to stabilize polycarbonates by adding mixtures of boric acid esters containing oxetane groups and phosphites. (See German Published Patent Specification No. 2,510,463 and the corresponding U.S. Pat. No. 4,102,959.)
With the exception of the use of stabilizer mixtures according to German Published Patent Specification No. 2,510,463, the stabilizing possibilities hitherto known have certain disadvantages when the polycarbonates are subjected to extreme conditions; in particular, either the effect of stabilizing the polycarbonates to heat is insufficiently high or the resistance to hydrolysis is insufficiently high.
It has now surprisingly been found that polycarbonates can be effectively stabilized to light and heat, without the addition of phosphites and without impairing the resistance of the stabilized polycarbonate to hydrolysis, by incorporating either boric acid esters containing oxetane groups, a mixture of a boric acid ester containing oxetane groups and a boron-free oxetane compound or a mixture of a boric acid ester which is free from oxetane groups and a boron-free oxetane compound.